The present invention relates generally to control of the operating height of a header of a mobile harvester and more particularly to automatic height control, responsive to a groundengaging feeler or follower, of a forward gathering portion of the header.
For convenience, discussion and description of the invention and the embodiment shown in the drawings will be limited to its application to a self-propelled combine harvester. It will be clear that the invention may be applied appropriately to other machines where there is a need to control automatically, movement and relative position of one functional element with respect to another, including the headers of tractor-drawn and tractor-mounted harvesters.
Automatic header height control systems are well known and are in wide commercial use in a number of forms. In harvesting certain crops, it is desirable to keep the crop gathering unit close to the ground to minimize losses. To maintain a selected gatherer-to-ground relationship by manual control is difficult and fatiguing. Automatic controls relieve the operator and, at least potentially, maintain a selected operating height more reliably and constantly.
Typically, one or more ground following feelers beneath the crop gathering unit are connected to the controls for a hydraulic or other power lift system so as to signal changes in operating height, with the power lift system responding accordingly. Automatic height controls may be applied to a "rigid" header in which the crop gatherer unit, possibly including a cutter bar, forms part of a rigid assembly, including a feeder house for delivery of crop to the combine body, the whole header being pivoted to the body for vertical movement pivoting about a transverse horizontal axis and controlled by the power lift system. In other arrangements, the crop gathering unit may have a forward floating portion such as a flexible cutter bar which rides on the field surface, header height being controlled automatically, responsive to the vertical disposition of the floating portion of the gatherer relative to the main portion or frame of the crop gathering unit. Another example of a gathering unit with a "forward floating portion" and where automatic height control is advantageous is a row crop harvesting header of the type disclosed in U.S. Pat. No. 3,808,783, Sutherland et al, also assigned to the assignee of the present invention.
Automatic height control systems now in use or proposed tend to be either somewhat crude and inherently unreliable or too sophisticated and complex to be commercially attractive. The simpler systems typically use cumbersome linkages to transmit relative movement from the ground follower or feeler to an actuator between a pair of limit switches which are necessarily exposed, at least partially, to possible mechanical damage and dust contamination. Selection of relative operating height set point is made by adjusting the linkage and/or repositioning the switches. A proposal to make selection of operating height set point more convenient involves the use of additional limit switches, each positioned to correspond to a particular operating height set point and electrical circuitry for selecting which limit switch is to be operative, but this system is also mechanically relatively complex and vulnerable in many harvesting environments. Other electronically or electrically more sophisticated systems have been proposed, including one in which each of a plurality of ground followers or feelers spaced across a transversely extending crop gathering unit is directly connected with a position switch or has an integral position switch at its pivot point with the gatherer frame. In combination with appropriate circuitry this provides the possibility of control modes other than the simple control mode inherent in the systems referred to above. However, the practicality and commercial feasibility of such systems must be questioned.
It is also known in a crop gatherer unit having a floating element, such as a cutter bar or row unit, to provide a mechanically actuated range indicator visible to the combine operator and representative of the vertical disposition of the floating element relative to the fixed portion of the gatherer.